The gizzard or gizzards ( Ventriculus muscularis , also Ventriculus pars muscularis ) is a thick muscle -equipped organ in the digestive tract of birds , reptiles , fish , and figuratively (not homologous) also with invertebrates (here mostly proventriculus called). It is also believed to be found in dinosaurs . Equipped with hard parts such as friction plates, strips or "teeth" and possibly with gastroliths (stomach stones), it serves to chop up food and thus as a kind of substitute for the chewing carried out in other animal groups by chewing (in the oral cavity with teeth ).
A separate gizzard is found mainly in herbivorous birds, especially grain-eaters.
In the bird's stomach, the gizzard is the second stomach after the glandular stomach ( ventriculus glandularis or proventriculus ). The gizzard of birds is lined with the gastric mucous membrane (tunica mucosa), beneath which sits a submucosal tissue (tela submucosa), followed by the actual muscle layer (tunica muscularis). Its wall consists mainly of smooth muscles . It can be anatomically divided into four separate muscles. The inner surface of the gizzard is lined by a tough, yellowish-green layer, the cuticula gastrica, which consists of solidified glandular secretions. It consists of the carbohydrate-protein complex Koilin, with properties similar to those of keratin . The cuticle serves as a grater on which the stomach stones (called gastrolites or grit) grind up the food.
Poultry gizzards are part of poultry and are used in Asian, African, Southern European, Hungarian and Jewish-kosher cuisine, including fried on salad or in soups.
Different lines of development of bony fish have developed gizzards convergent to one another. In almost all cases, these are herbivorous species, rarely users of dead plant matter (detritivores). Muscle gizzards exist in numerous representatives of the mullet (Mugilidae), surgeon fish (Acanthuridae) and rodent perch (Girellidae). At least the mullets also sometimes use gastrolites.
Among the living (recent) reptiles, only one group has a muscular gummy stomach: the crocodiles . Although these also take up stomach stones, a function for the development of food for them has been denied and seems unlikely today.
The existence of a gizzard in sauropod dinosaurs was mainly inferred from the finding of gastroliths, mostly polished pebbles, in the fossil skeletons. According to more recent studies, however, a function of the gastric stones seems very unlikely for this purpose. The oviraptosaur caudipteryx and the theropod sinornithomimus , for example, offer indications of this function . This points to the formation of the gizzard in the extended trunk group of birds.
- ↑ Volker Storch, Ulrich Welsch: Kükenthal - zoological internship. Spektrum Akademischer Verlag, 2009, ISBN 978-3-8274-1998-9 , pp. 117, 215, 228, 247, 255-257, 357, 401.
- ↑ Hans-Georg Liebich: Functional histology of domestic mammals and birds: textbook and color atlas for study and practice. Schattauer Verlag, 2010, ISBN 978-3-7945-2692-5 .
- ^ IJ Harrison, H. Senou: Order Mugiliformes. Mugilidae. Mullets. In: KE Carpenter, VH Niem (Ed.): FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Volume 4: Bony fishes part 2 (Mugilidae to Carangidae). FAO, Rome 1997, pp. 2069-2108.
- ↑ David H. Evans, James B. Claiborne: The Physiology of Fishes. (= CRC Marine Biology). 2nd Edition. CRC Press, 1997, ISBN 0-8493-8427-3 , p. 52.
- ↑ GM King: Reptiles and Herbivory. Springer Verlag, 1996, ISBN 0-412-46110-2 .
- ↑ Michael A. Taylor: Stomach Stones for Feeding or Buoyancy? The Occurrence and Function of Gastroliths in Marine Tetrapods. In: Philosophical Transactions of the Royal Society London B vol. 341 no. 1296, 1993, pp. 163-175. doi: 10.1098 / rstb.1993.0100
- ↑ Oliver Wings: A review of gastrolith function with implications for fossil vertebrates and a revised classification. In: Acta Palaeontologica Polonica. 52 (1), 2007, pp. 1-16.
- ↑ Oliver Wings, P. Martin Sander: No gastric mill in sauropod dinosaurs: new evidence from analysis of gastrolith mass and function in ostriches. In: Proceedings of the Royal Society. B 274, 2007, pp. 636-640. doi: 10.1098 / rspb.2006.3763